The present invention relates to a method for quantifying a substrate included in a sample solution.
The following describes a method for quantifying glucose as one example of the substrate.
As a conventional electrochemical method for quantifying glucose, a method which employs a combination of a reaction layer including glucose oxidase (EC1.1.3.4, hereinafter referred to as GOD) with an oxygen electrode or a hydrogen peroxide electrode is well known (for example, `Bio-sensor` edited by Shuichi SUZUKI, Kodansha).
GOD uses oxygen as an electron acceptor and selectively oxidizes the substrate, .beta.-D-glucose, to D-glucono-.delta.-lactone. Accompanied by this reaction, oxygen is reduced to hydrogen peroxide. The amount of glucose is determined by measuring the amount of consumed oxygen with the oxygen electrode or alternatively measuring the amount of generated hydrogen peroxide with the hydrogen peroxide electrode.
However, as presumed from the reaction process mentioned above, the result of this method is significantly affected by a concentration of oxygen dissolved in a sample solution. Especially, measurement is even impossible under an oxygen-free condition.
Novel glucose sensors have accordingly been developed, in which an organic compound or a metal complex, such as potassium ferricyanide, a ferrocene derivative or a quinone derivative is used in place of oxygen as the electron acceptor. This type of sensor oxidizes the electron acceptor, which has been reduced by an enzyme reaction, with the electrode and determines a concentration of glucose based on its oxidizing current. This system enables known amounts of GOD and the electron acceptor to be stably and accurately carried on a electrode system, and to integrate the electrode system and a reaction layer in a state similar to the dry state. Disposable glucose sensors based on this technique can readily determine a concentration of glucose only by introducing a sample into a sensor chip connected to a measurement device, and accordingly have been noted recently. This technique is applicable not only to a quantification of glucose but to a quantification of another substrate, and is extensively studied. This technique, which utilizes such an electron acceptor and integrates the electrode system and the reaction layer, enables simple electrochemical quantification of the substrate.
For the quantification of the substrate, such as blood sugar value, a novel quantifying method with high accuracy has been highly demanded.